Fan tip clearance in an axial flow fan has a considerable effect on fan efficiency. For example, an axial flow fan with a tip clearance of 2% of the fan diameter will only produce about 60% of the pressure of a fan unit with a tip clearance of 0.1% of the diameter of the fan. Large tip clearances can produce premature stall conditions in the fan blades due to turbulent flow, particularly at the outer extremity of the fan blades where a higher percentage of the work is done on the air. Large tip clearances also contribute substantially to noise generation.
Small tip clearances in axial flow fans have been obtained by casting an axial flow fan barrel and machining the inside surface of the barrel so that its centre is concentric with the fan shaft centre and its diameter is very close to the diameter of the fan. Axial flow fans may also be formed by metal spinning where the centre of the formed barrel is concentric with the fan shaft centre. Other methods include using rings which support the fan in the barrel and which are shiftable to permit placing of the axis of the fan coincident with the axis of the barrel. These methods produce acceptable axial flow fans, however, they are very costly and complex.
With the above methods of manufacturing axial flow fan barrels, a compromise is usually reached between optimizing the configuration of the barrel and reducing the manufacturing costs. This results in the manufacture of axial flow fan barrels which have larger than desired tip clearances, undesirable noise generation and a less efficient fan.
It is therefore an object of the invention to provide an easy-to-assemble barrel for an axial flow fan which provides minimum tip clearance with resultant increase in efficiency and performance and reduction in noise generation at a relatively low cost of manufacture.
It is another object of the invention to provide a barrel assembly which may be dimensioned for use in large and small axial flow fans.
It is a further object of the invention to provide a barrel assembly for an axial flow fan which is readily assembled and retains its shape.
It is yet another object of the invention to provide an insulated cabinet for an axial flow fan barrel assembly where the insulation structurally supports the barrel assembly in the cabinet and which dampens most noise and vibrations produced by the fan.
It is another object of the invention to provide an insulated cabinet enclosure for an axial flow fan barrel where the insulation structurally supports the barrel assembly in the cabinet and absorbs shock loads.
It is another object of the invention to provide a method for insulating a cabinet enclosing an axial flow fan barrel assembly.
It is another object of the invention to provide a vane assembly for an axial flow fan which has evenly spaced-apart, equally radially-extending vane members.